import java.util.Scanner;//1302: 【入门】是否适合晨练？

public class Main1302 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int t = sc.nextInt();
        if (20 <= t && t <= 30){
            System.out.println("OK");
        }else {
            System.out.println("NO");
        }

    }
}
